All 19-year-old Valentin Castellanos needed was three training sessions to earn his first start — and in his MLS debut, no less.

He needed just 46 minutes last Saturday to score his first goal. Not a bad way to reward head coach Domenec Torrent’s decision in New York City FC’s 2-2 draw against the Vancouver Whitecaps.

“Like I mentioned after the match on Saturday, I’m very fortunate for the opportunity, and I’m glad I’m feeling comfortable with my teammates,” said Castellanos, a native of Argentina, through a translator after Tuesday’s training session.

Torrent said the choice to start Castellanos — nicknamed “Taty” — immediately after his arrival was similar to the way they do things with new players in Europe. For some, it was a shock. For Torrent, it was business as usual.

“I don’t understand why people say, maybe because I don’t know, maybe we’re supposed to wait two weeks, three weeks, explain to me why,” Torrent said Tuesday. “When you feel that a player is ready to play, he plays. For me, it’s not a surprise.”

Castellanos trained with Torrent last year at NYCFC’s parent-club Manchester City. The Blues’ first-year coach had been an assistant under manager Pep Guardiola at the time.

“He’s a great coach and a great person,” Castellanos said. “I’m definitely going to take advantage of his knowledge to get better as a player.”

Castellanos has come a long way from Atletico Torque of Uruguay, which sent him on loan to NYCFC at the end of July. Playing in Yankee Stadium, let alone his first time ever in New York City, is a massive culture shock from the smaller stadiums in which he once played that could only fit friends and family.

“The changes from the field, to the fans, to even the media, are something you don’t see back in Uruguay at a small city at a small market, but it’s very different here in New York,” he said. “It’s very surprising. It’s a culture shock, but I’m happy to be here.”